The SI could be a smuggler who crosses paths with Anakin during one of his missions. They team up and the SI shows Anakin a different side of the galaxy, one that's not all about the Jedi and Sith. This could make Anakin question his place in the galaxy and his loyalty to the Jedi Order. Their adventures together could range from dealing with pirates to uncovering ancient secrets.
One idea could be Anakin as a Sith having to face his former Jedi allies. He might struggle with his new identity while still having remnants of his Jedi self. For example, he could be sent on a mission by the Sith to destroy a Jedi stronghold but find himself hesitating when he sees his old friends there.
One plot idea could be that your SI OC is a young Force - sensitive being discovered by the Jedi Order, but they have a connection to an ancient Sith prophecy. The Jedi must decide whether to train them or fear their potential for darkness. Another idea is that your OC is a bounty hunter who gets caught in the middle of a power struggle between the Hutts and a new criminal syndicate. They have to use their wits and skills to survive and maybe even tip the balance of power.
Perhaps a fanfiction where Anakin, as a Sith, is sent on a mission by Palpatine. But on this mission, he meets a young Force - sensitive who reminds him of his own past. This makes him start to have doubts about the Sith ways. He begins to secretly teach the young one about the Force in a more balanced way, all while trying to hide it from Palpatine.
One idea could be that Anakin's spirit somehow guides Rey in her Jedi training. Maybe he appears to her in visions and imparts his unique knowledge of the Force, especially the more unorthodox aspects he learned during his time. Another plot could involve Rey finding an ancient artifact that was once connected to Anakin, and through it, she uncovers secrets about his past that help her in her fight against the new Sith threat.
Maybe a story where Ahsoka has a premonition about Anakin's fall to the dark side. She tries to prevent it in secret, which leads to all sorts of dangerous situations and moral dilemmas as she struggles with whether to tell the Jedi Council or handle it on her own.
A third plot idea is that Anakin travels to different points in time during key battles in the Star Wars universe. He could use his skills to turn the tide of battles that were lost in the original timeline. For example, he could go back to the Clone Wars and help the Republic win a crucial battle, or he could jump forward in time to assist the Resistance against the First Order. His time - traveling abilities would make him a wild card in these battles, and his presence could rewrite history.
Well, a cool plot for a Star Wars Mandalorian SI fanfiction could involve the self - insert being a former Jedi in hiding. They could use their Jedi training secretly to help the Mandalorian and Grogu. Maybe they teach Grogu some new skills that are a blend of Jedi and Mandalorian ways. Also, the self - insert could have a past connection to the Sith, which adds an interesting layer of conflict as they struggle not to be drawn back to the dark side while helping the Mandalorian. Another idea is that the self - insert is an artist who uses their art to document the adventures of the Mandalorian, and in the process, their art gains some sort of magical or important significance in the Star Wars galaxy.
One idea could be a story where Anakin and Barriss are forced to team up on a mission to a remote planet. They start off distrusting each other due to their different beliefs and allegiances within the Jedi Order. But as they face various challenges like dangerous native creatures and a Sith - influenced local warlord, they gradually learn to understand and respect one another.
One idea could be exploring a mission that Ahsoka and Anakin go on where they get stranded on an unknown planet. They have to rely on each other's skills to survive and in the process, Anakin imparts some deeper Jedi wisdom to Ahsoka. Another could be a story set during the Clone Wars where they face a new and powerful Sith enemy together, forcing them to combine their fighting styles in a unique way.
One idea could be an OC Jedi who discovers a long - lost Jedi technique that gives them unique powers. This could lead to a series of adventures as they try to master it while also facing off against Sith or other enemies who want to steal the knowledge for themselves.